This invention relates to liquid development systems for electrophotography and, more particularly, to a new and improved liquid development system utilizing self-contained cartridges for handling liquid electrophotographic developers.
Conventional liquid developer systems have several inherent problems. As liquid developer is used, it must be replenished, but replenishment by the operator involves possible spillage of liquid developer in the interior of the electrophotographic system or the surrounding office environment. Moreover, circulation of liquid developer from a reservoir within the apparatus to the electrophotographic material being developed is often accomplished by a central pump which distributes the developer to the electrophotographic surface through a manifold, creating nonuniform flow with unequal velocity and pressure distribution, resulting in observable print defects.
Furthermore, as liquid developer is used, the toner concentration in the developer decreases, resulting in decreased density of the developed images. Another difficulty with conventional liquid developer systems results from evaporation of liquid when the developer system is not in use, causing plating-out, leaving a dry toner deposit on surfaces of the developer system, and also depleting the liquid content of the developer in the system. Such depletion causes toner particles to aggregate, resulting in print defects.
Moreover, where liquid toner has been supplied in cartridges for use in electrophotographic systems, cartridge replacement has resulted in spillage of liquid remaining in the cartridge and also requires disposal of that liquid. Furthermore, evaporation of the developer liquid during use in conventional cartridge systems not only depletes the volume of the developer and shortens the life of the cartridge, but also requires complex filter arrangements to trap all of the evaporated developer to be trapped within the electrophotographic apparatus to avoid contaminating the surrounding atmosphere.